The present invention relates generally to semiconductor fabrication and, more particularly, to a method and apparatus for reducing consumption of fluid delivered to a backside of a substrate during a cleaning operation.
Cleaning chemistries for single wafer cleaning operations are formulated for specific applications and are designed so that a small amount of the chemistry applied to the surface of the wafer is sufficient for cleaning the surface of the wafer. That is, a thin film of the fluid supplied to the surface of the wafer produces the desired cleaning effects. Because of the high costs for the purchase and the disposal of the cleaning chemistries, it is desired to only use the amount of chemistry that is necessary for effective cleaning.
Applying a thin film of the cleaning chemistry to a top surface of a semiconductor substrate is easily accomplished as gravity is working to assist the process. A small amount of fluid can be puddled on a top surface of the substrate and the substrate can be rotated around its axis to spread the fluid over the surface of the substrate without spinning the fluid off of the wafer surface. The speed of the rotation can be used to control the thickness of the fluid layer. However, the cleaning chemistry can not be applied to the backside of the wafer in this manner as the fluid will be lost. FIG. 1 is a schematic diagram of a wafer having cleaning chemistries applied to a top and a backside of the wafer. Wafer 100 has a thin film applied to a top surface of the wafer by top nozzle 104a. However, bottom surface 106 can not retain the fluid from bottom nozzle 104b, where as much as 95% of the fluid delivered to bottom surface 106 can be lost. Thus, conventional spray-on techniques are not effective for low-volume chemistry cleaning of the wafer backside.
One attempt to minimize the fluid loss associated with cleaning the backside of the wafer is to clean the top side of the wafer and then flip the wafer over to clean the other side. However, the throughput for the cleaning process is cut in half since the cleaning is performed sequentially. Accordingly, this alternative is not a viable one. Another attempt to address the shortcomings of the prior art is to provide a reservoir containing the cleaning chemistry and place the backside of the wafer in contact with a meniscus formed by the cleaning chemistry. FIG. 2 is schematic diagram of a wafer coming into contact with a meniscus of a cleaning solution in a reservoir. Bottom surface 106 of wafer 100 is brought into contact with meniscus 108. Meniscus 108 is formed when the cleaning chemistry is filled to the top of reservoir 110. However, a shortcoming with the use of a reservoir is due to each of the cleaning solutions having different surface tensions. Thus, the meniscus height can be different for each of the cleaning chemistries. Consequently, the distance for the wafer to be brought into contact with the cleaning chemistry will change with the different cleaning chemistries. This configuration is also difficult to implement mechanically. Additionally, the contents of reservoir 110 will have to be changed over time as the cleaning chemistry becomes dirty, which negatively impacts throughput and control of contaminants.
In view of the foregoing, there is a need for a method and apparatus for reducing the volume of cleaning chemistry applied to the backside of a wafer in a single-wafer cleaning tool in a manner that does not negatively impact the throughput or defect rate.
Broadly speaking, the present invention fills this need by providing a nozzle and delivery system for applying a minimal amount of fluid to the backside of a semiconductor substrate. It should be appreciated that the present invention can be implemented in numerous ways, including as an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.
In accordance with one aspect of the present invention, a nozzle is provided. The nozzle includes an inner cylindrical tube having a top opening and a bottom opening. An upper cap overlying a top portion of the inner cylindrical tube is included. The upper cap is moveably disposed over the inner cylindrical tube. The upper cap includes a top with at least one hole defined therein. The top includes a sidewall extending therefrom.
In accordance with another aspect of the invention, a fluid delivery system for cleaning a backside of a semiconductor substrate is included. The fluid delivery system includes a shaft configured to rotate about an axis of the shaft. An arm having a first end and a second end is included. The first end is affixed to the shaft and is in communication with a fluid source. A cap moveably disposed over the second end of the arm is included. The cap has a top with at least one hole defined therein. The top includes a sidewall extending therefrom. The sidewall extends over a portion of the second end of the arm.
In accordance with yet another aspect of the invention, a method for reducing an amount of a cleaning chemistry applied to a backside of a wafer during a cleaning operation is provided. The method initiates with positioning a nozzle having a moveable top under a backside of a wafer to be cleaned. Then, a fluid flow occurs through the moveable top to raise the moveable top into close proximity with the backside of the wafer. Next, a fluid barrier is created between a top surface of the moveable top and a backside of the wafer while the fluid flows through the moveable top. Then, the backside of the wafer is cleaned by the fluid barrier.
It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.